Ultraviolet light is very effective for killing some germs. Airborne bacteria and bacteria on the outer surface of an item are easily killed by UV light. Germs that are under the surface or that are not in the direct path of the UV light are not easily killed. For UV light radiation to be effective the germs have to be exposed to high levels of UV radiation for a short period of time or exposed to low level UV for a longer time.
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Ultraviolet light is part of the electromagnetic spectrum with wavelengths from 10 nanometres to 400 nanometres. UV is divided into long wavelength, medium wavelength and short wavelength frequencies. Medium wavelength UV radiation is the light that is used to disinfect food, air, water and the surface of objects such as surgical utensils. UV lamps come in several different types according to their intended use. Some UV lamps emit long wavelength UV light. You probably have seen a black light lamp at some time. Black lights emit long wave UV.
How It Works
Medium wavelength UV light, between 300-100 nanometres, kills microorganisms because it has a mutagenic effect on them. This wavelength of light has an energy level per photon emitted of 4.13 to 6.20 electron volts. UV light in this range breaks down the DNA structure of microorganisms exposed to it and prevents them from reproducing, effectively killing the organism. UV radiation is known to be effective against bacteria, moulds and parasites such as dust mites and lice. Staph, perfigens, and E. coli are killed by UV radiation as are tuberculosis and viral infectious agents. Upper room air disinfection is crucial in many parts of the world due to severe acute respiratory syndrome (SARS) and tuberculosis infection. In Africa and Asia ultraviolet germicidal irradiation (UVGI) is effectively being used to combat infection from tuberculosis and SARS. According to the National Institutes of Health upper air UVGI disinfection is effective in reducing tuberculosis infection in a hospital setting.
Disinfecting the Air
UVGI lamps are being used to kill microorganisms in the air In many health care facilities and other public buildings. According to Dave Shagott in "Alternate Methods for Using Germicidal UV-C Disinfection Lamps to Supplement HEPA Filtration," portable UV modules mounted on the clean air outlet of a room are very effective at killing airborne organisms. UV modules installed inside the building duct works can effectively sterilise the air in the entire building. UV modules are mounted near the coils in HVAC systems to prevent bacterial growth in that cool, moist environment.
Laboratories, hospitals and college research facilities utilise UV light to sterilise equipment, clothing, and utensils. Many labs and hospitals use UV cabinets with a 254 nanometre UV lamp installed on each shelf to disinfect Petri dishes, beakers and other small utensils. Handheld UV-C lamps are used to disinfect surfaces in facilities such as nursing homes. The portable UV lamps are effective at killing microorganisms on surfaces, beds and areas such as showers and bathroom fixtures. These lamps are also effective for killing dust mites and louse eggs.
Water treatment facilities employ UV lamps as part of the water treatment process. It is not effective alone because UV light won't penetrate far beneath the surface of murky waste water. UV sterilisation systems are also being used effectively to disinfect drinking water. Homeowners can install UV lamps to disinfect well water and other sources of potable water. Public water facilities are also installing UV systems in their systems at various locations to combat germs in drinking water. After 9-11, many public water facilities installed UV disinfection equipment as a defence against accidental contamination or intentional contamination of drinking water by terrorists.
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